Frictional drag reducer for immersed bodies



Nov. 14, 1967 J. A. BURKHARDT PRCTIONAL DRAG REDUCER FOR IMMERSED BODIES FIC-3.5.

PERMEABLE WEBBING FIG'.

IN VEN TOR.

JOSEPH A. BURKHARDT,

ATTORN E1 United States Patent O 3,352,118 FRICTIONAL DRAG REDUCER FOR IMMERSED BODIES Joseph A. Burkhardt, Houston, Tex., assignor to Esso Production Research Company Filed Aug. 11, 1965, Ser. No. 478,965 8 Claims. (Cl. 61-46) ABSTRACT F lTHE DISCLOSURE A double wall sleeve or sack having permeable elastic webbing connecting the walls to each other surrounds a body immersed in water to reduce frictional drag of such body when it is subjected to Wave and/or current forces by streamlining the outer contour thereof. A constant volume fluid is contained between the two Walls. Under the action of drag forces, the outer Wall deforms and contracts toward the leading edge of the body and elongates from the trailing edge thereof.

The present invention relates to method and means for reducing frictional drag of bodies immersed in a flowing stream. More particularly, the invention concerns method and means for reducing the frictional drag coeflicient of cylindrical piles immersed in a flowing stream. The piles extend above the level of the stream and are imbedded in the ground underlying the water. They are preferably the type used to support offshore oil and gas drilling platforms.

Piles used to support offshore structures are often subjected to strong wave action and currents and, accordingly, must be constructed With sufficient strength to withstand such forces.

The present invention permits reduction in the strength requirements of these piles, and, thereby, a reduction .in the cost of offshore platforms.

Essentially, the invention achieves a reduction in the frictional drag coefficient of bodies .immersed in a flowing stream (or moving in a still stream) by streamlining the outer contour of the body. For the streamlining to be effective, it is essential that the streamline be properly oriented in the stream. In addition, for variable flow such as that which occurs about a fixed column in lthe ocean, the orientation of the streamline must be automatic or self-induced by the flowing stream.

An object, then, of the present invention is to provide apparatus and method which permits the flowing stream to alter the effective contour of an immersed body into a streamlined contour and to present this streamlined contour always in proper orientation to the stream.

These and other objects and advantages of the invention will be apparent from the following description thereof when taken with the drawings in which:

FIG. 1 is a view in front elevation;

FIG. 2 is a sectional view taken along lines 2--2 of FIG. l;

FIG. 3 is a view taken along lines 3 3; of FIG. 2; and

FIGS. 4 and 5 are similar to FIG. 2, but illustrate the streamlined contour under different directions of the flow stream.

Referring to the drawings in greater detail, in FIG. 1 is shown an elongated member or pile immersed in a body of water 11. Pile 10 is preferably cylindrically congured. It is imbedded in the land 12 underlying water 11 and supports at its upper end a portion of an offshore platform 13.

As seen also in FIGS. 2 and 3, an elongated deformable double-wall sack or sleeve 14 ext-ends from above the level of water 11 a substantial length of pile 10. Sleeve 14 includes an inner nondeformable cylindrical ice wall 15 arranged adjacent the outer wall of pile 10 and attached to an outer, deformable cylindrical wall 16 by an elastic, permeable webbing 17. A constant volume, incompressible, Newtonian fluid, preferably water or oil, is placed within walls 15 and 16 and fills the space therebetween. Thus, outer wall 16 is anchored to inner wall 15 and to pile 10 by the multiplicity of elastic members 17.

In a nonmoving stream, the deformable sleeve 14 assumes a shape as seen in FIG. 2 of minimum elastic energy, a circular cylinder concentric with the cylindrical pile 10. As seen in FIGS. 4 and 5, when the stream moves,

, the Vdeformable cylinder consisting of outer Wall 16 is forced by drag forces to contract toward the leading are of the cylindrical surface of the pile 10 and to elongate from the trailing edge. The volume of fluid contained in the space between the deformable and nondeformable walls 16 and 15, respectively, is fixed and as the deformation occurs, the surface area and the elastic energy of the deformable cylindrical Wall 16 increases. Wall 16 is impermeable, and consequently, the flowing stream cannot penetrate the membrane which is a characteristic of a streamline. Under the action of a moving stream, the outer wall 16 is caused to deform and its deformation will assume a contour of minimum elastic energy which will also be a contour of lesser drag within the restraint that the contour must enclose a constant volume. As the velocity of the stream alters, the contour of the deformable wall 16 changes. The elastic force of the membrane is in equilibrium with the drag force of the stream on it. The elastic energy of the membrane 16 will tend to describe a contour of minimum area within the three restraints of 1) constant volume contained by the contour; (2) minimum surface area as related to stress strain behavior of the membrane material; and (3) the drag forces induced by the flowing stream.

Suitable materials that may be employed as the deformable wall membrane 16 and as the nondeformable wall membrane 15 and as the elastic webbing are rubbers, plastics, metals and/or combinations of the three groups of materials as laminates, meshes and/or Webs.

Having fully described the operation, apparatus, objects, and advantages of my invention, I claim:

1. A water-based structure including a pile positioned in a body of water and extending above water level cornprising:

sleeve means adapted to contain a constant volume fluid surrounding said pile and extending from below to above the water level, said sleeve means comprising an inner well, an outer wall deformable by wave and/or current forces, an elestic means interconnecting said inner and outer walls whereby said outer wall is forced by drag forces to contract toward the leading edge and to elongate from the trailing edge of said pile when said wave and/ or current forces act on said pile.

2. A structure as recited in claim 1 in which said elastic means comprises permeable webbing connected to said inner and outer walls.

3. A structure as recited in claim 2 in which said constant volume uid is oil.

4. A structure as recited in claim 2 in which -said constant volume fluid is water.

5. A water-based structure comprising:

a platform supported above a body of water;

a plurality of piles positioned in said water and supporting said platform;

sleeve means surrounding each of said piles and extending from below to above the water level, said sleeve means comprising an inner wall, an outer wall deformable by wave and/or current forces, a constant volume fluid contained between said inner 3 4 and outer walls, and elastic means interconnecting References Cited said inner and` outer walls Awhereby said outer Wall is forced by drag forces to contract toward the lead- UNITED STATES PATENTS ing edge and to elongate from the trailing edge of `said ypile when said wave and/or current forces act 934176 9/1909 H ubbard 61-54 Von Said pik" 3,177,667 4/ 1965 Liddell 61-54 6. A structure as recited in claim 5 in which said elastic rmeans comprises permeable .webbing connected to FOREIGN PATENTS said inner and outer Walls.

7. A structureas'rec'ited in claim 6 in which said con- 10 454661 8/1950 Italy' stam Volume 'll-1d s 011 JACOB SHAPIRO, Primary Examiner.

8. A structure as recited in claim 6 in which said constant volume luid is Water. 

1. A WATER-BASED STRUCTURE INCLUDING A PILE POSITIONED IN A BODY OF WATER AND EXTENDING ABOVE WATER LEVEL COMPRISING: SLEEVE MEANS ADAPTED TO CONTAIN A CONSTANT VOLUME FLUID SURROUNDING SAID PILE AND EXTENDING FROM BELOW TO ABOVE THE WATER LEVEL, SAID SLEEVE MEANS COMPRISING AN INNER WELL, AN OUTER WALL DEFORMABLE BY WAVE AND/OR CURRENT FORCES, AN ELESTIC MEANS INTERCONNECTING SAID INNER AND OUTER WALLS WHEREBY SAID OUTER WALL IS FORCED BY DRAG FORCES TO CONTRACT TOWARD THE LEADING EDGE AND TO ELONGATE FROM THE TRAILING EDGE OF SAID PILE WHEN SAID WAVE AND/OR CURRENT FORCES ACT ON SAID PILE. 